The example embodiments relate to the printing and marking arts. They particularly relate to printing systems with multiple processing units providing substantial degrees of freedom in performing print jobs, and to print job scheduling for such printing systems. However, the following relates more generally to printing and marking systems of all types, and to print job scheduling and bottleneck obviation for same.
Printing systems have generally been designed with a strong emphasis on ease of use, and a lesser emphasis on exploiting to the fullest the capabilities of the underlying printing hardware. Accordingly, the user is typically given a few pre-selected controls each having a limited number of pre-selected settings. For example, an image contrast control may have a “photo-optimized” setting, a “graphics-optimized” setting, and a “text-optimized” setting.
Additionally, printing systems have generally employed only one or a few sheet paths, and only one or a few print job destinations. For example, a typical printing system may have a single marking engine, which bottlenecks sheet processing down to a single print path. Even if multiple marking engines are provided, the print media conveyor may be configured to limit sheet processing to a single print path. In such an arrangement, the print jobs are queued and performed sequentially, in a first in-first out (FIFO) sequence.
Some more advanced printing systems provide multiple sheet paths and multiple job destinations. For example, a single job scheduler can be linked with two printing systems (tandem printing), or with three or more printing systems (cluster printing). FIFO print job queue/processing is typically employed; however, since multiple printing systems are linked to the job scheduler, the job scheduler can divide up sheets of a given job amongst two or more of the linked printing systems, so as to more efficiently process the print job. In tandem and cluster printing, each printing system is an independent printing system; accordingly, the sheets of a print job that is executed by two or more printing systems are manually collated or combined. FIFO print job queue/processing does not fully leverage the capabilities of multiple marking engines provided in tandem printing, cluster printing, and other parallel printing systems.
Integrated printing systems with multiple types of marking engines, such as color and black only engines, can assemble documents comprised of a mixture of the different IME type outputs. Productivity of such systems is optimal when documents to be assembled have a fairly uniform distribution of page types with the ratio of page type being roughly proportional to the productivity or capability of the IME types. However, severe productivity bottlenecks occur when the page type distributions within a sequence of consecutive pages of a job are substantially disproportionate from the production rate of the page types.